An industrial reactor often contains one, two, and even more than two dispersed phases, and the distribution of dispersed-phase particles in the reactor is an important reflection of the performance of the reactor and is also an important basis of the design and amplification of the reactor.
In an invasive photogrammetric technology developed in recent years, a measuring instrument (probe) with a photographing function extends into the reactor directly to conduct online photographing on multiphase fluid that moves at high speed at a measured point, and image processing software is utilized for identifying, processing and counting the dispersed-phase particles, thereby obtaining concentration and particle-size distribution of the dispersed-phase particles at the measured point. The method is intuitive and accurate. Currently, this kind of technology mainly includes an optical photographing probe technology from German SOPAT Company, a PVM (Particle Video Microscope) technology from American Mettler Toledo Company and a multiphase measuring instrument based on a telecentric photographing principle from Institute of Process Engineering, Chinese Academy of Sciences. In the invasive photographing technology, the difference of gray values of all phase states of medium images in a picture is a core problem for accurately identifying all phases and further obtaining accurate measurement results. According to an imaging principle of a camera, light reflected from a surface of a scenery converges on a photosensitive region of a film or an image sensor by a lens to form a latent image, and gray of the latent image depends on lighting conditions (intensity, colors and irradiating directions) and surface properties (colors, shapes and roughness and the like) of a photographed object. Under common photographing conditions (fixed light intensity and color, and front irradiation), reflection of the continuous phase (usually water solution) in the multiphase system to light rays is weak, and luminosity is low, so the gray value of the latent image is small. In this way, the stronger the reflection of the dispersed phase particles to the light rays is, the higher the luminosity is and the larger the gray value of the latent image is, so the dispersed-phase particles are in sharp contrast with the continuous phase in the picture and can be easily and accurately identified and processed by the image processing software. This is a basis of successful application of the invasive photographing technology.
While in actual measurement, the dispersed-phase particles in many systems are low-luminosity dark solid particles or/and bubbles. At the moment, gray values of the latent images of the continuous phase and the dispersed phase in the picture are lower and an obvious gray difference cannot be formed, so that an identification degree of all the phases in the picture is poor and all phases of media cannot be identified and processed by the image processing software. A more direct method is to increase the intensity of illumination, but with a purpose of reducing invasive errors as many as possible, it is impossible to install more LED lamps or illuminating optical fibers on the invasive photographing probe. In addition, over-high illuminating intensity can also cause internal heating, so the problem is hard to solve by increasing the illuminating intensity. In a common method for actual measurement, a reflecting board or backside illumination is added at an opposed side of the measured point in front of the probe, and by change of an illuminating environment of the measured region, the gray value of the latent image of the continuous phase on the picture is greatly increased, the gray value of the dispersed-phase particles is greatly reduced and a strong contrast is formed on the picture, thereby achieving identification of the two phases. However, discovered from practices, the addition of the reflecting board can cause a larger invasive error, and especially when a direction of an incoming flow at the measured point and the probe form an included angle of 180 degrees, the reflecting board blocks the incoming flow, causing serious measurement errors.
Mie scattering theory is based on the interaction of electromagnetic waves and charges that form substances. A particle group composed of many molecules is used as a multistage subgroup and is excited by incident waves to form a vibratory multistage subgroup which then radiates secondary wavelets outwards. Theoretically, amplitudes of all stages of wavelets are convergent series, and a sum of squares of the series in a specific direction is scattering light intensity in this direction.